Cobra Exhaust Tuning Recommendation.

In an ideal world it would be good to have regular access to a consistent Dyno and to make multiple changes/modifications to the Cobra exhausts to test and measure the results to make comparisons/conclusions.......

In the real world I do not have access to such luxuries....

My Aim is, and always has been, to try and claw back some of the lost BHP caused by the Cobra Exhausts installation (no matter how small an amount).

I am sticking with the standard front headers as this is what the Cobras are designed for and I already own them.

I am not going to mess with the Cobra front end collectors to try and create better balance/scavenging, I believe some gains might possibly be made, but, there is no guarantee of any success plus the monetary/time costs would be quite high....

I really do not like the solid disc in the central perforated baffle tube at all, I have decided to focus on this area, I have drilled a 16mm hole in each of the four exhausts in the centre of each solid plate disc, this will reduce the large restriction in this area, it will now allow two paths for the exhaust gas to exit the exhaust, the original gas path from inside to outside back to inside of the perforated baffle tube and also a second path straight through the solid disc and out....

I am expecting the noise levels of the exhaust to increase which might not be ideal, I have yet to start the bike up and have only just completed the modification. Looking forward to testing the bike soon......

Out on the bike this morning, first impressions, little more noisy but hardly noticeable (Was not exactly quiet in the first place...), seems to rev easier/faster but early days and only a fairly short ride....

Next step if happy with the new mods is to drill/enlarge the holes in the solid discs from 16mm to 21mm (final size)....


My thoughts/comments on direction and mods:

As discussed, very little hard data available featuring the Cobra Exhausts.....
As discussed, very hard to find hard data on VMax 4 into 4 Exhausts (Other than Cobras)......

Only really two main options with exhaust modifications, merged collectors entry or de-restricting the internals....

No evidence of anyone successfully modifying the collectors, no proof this will work, mostly merged collectors are featured/popular on 4 into 2 pipes, not 4 into 4 at all.... Often balance pipes are used for smooth running/mid range, not exactly high performance..... Expensive in time and money to modify and no history or high likelihood of success.....

On close internal inspection of the Cobras, very likely that they are highly restrictive due to bad design and cheap manufacturing practices.... History of similar modifications with very little data, cheap and easy and quick to modify.....

Interesting relevant data on 4 into 4 exhausts:

Ref: http://www.vmaxforum.net/showthread.php?t=44187

Above link shows standard engine, standard front headers, no merged collectors, no balance pipe, 4 into 4 exhausts, 1/4 mile ticket and runs at 11.5 and 117 mph, exactly the same times and speeds quoted of a standard VMax in the Haynes manual..... This suggests that this bike does not drop 13 BHP like the Cobras........


One other VMaxxer in the UK is running 4 into 4, moto-gp replica mufflers, no baffles, standard front headers, virtually standard engine, ignition upgrade, carbs upgrade pulling around 120 BHP.....

The above two examples suggest that the issue lies with the Cobra exhausts not with the merged collectors or the balance pipe......

Neither of the above two examples have the same or similar highly restrictive internal baffle system (tortuous path) of the Cobras.....

I don't believe you're going to find much if any of the lost HP with no amount of rework to the mufflers. They have enough flow capacity even though you think they are restrictive. The typical 4-1 mufflers have 1.5" (standard Kerker) outlets and perform just fine. The competition baffle allows an increase to the 2.5" outlet which gives a slight increase in power though the biggest gain is in the sound volume and tone and why people tend to install it.

I think you have to compare apples to apples in making comparisons.

The Facts as I understand them are below:

We are looking at a true 4 into 4 exhaust with the cobras, in combination with the original standard front headers.

Using the standard VMax with standard 4 into 2 exhaust as the performance benchmark. QTR Mile time = 11.5 Secs. Terminal Speed 116 Mph.

Reference this Vmaxforum thread: http://www.vmaxforum.net/showthread.php?t=44187

This is also a true 4 into 4 exhaust, not cobras, consistently runs the same standard VMax benchmark Qtr Mile times and Terminal speeds.....
Standard engine, same standard front headers, no crossover/balance pipes/scavenging, no modified collector, very little in the way of baffles.....

Clearly the referenced VMax above consistently duplicates the standard VMax benchmark performance for QTR Mile Power and Speed.
Clearly the referenced VMax above has a true 4 into 4 exhaust like the Cobras, with standard front headers, with no modified collector box and no scavenging.
Clearly the obvious difference between the referenced VMax above and a standard VMax with Cobra exhausts is minus 13 BHP and restrictive internal Cobra baffles.....

To compare track times you need a hell of a lot more info if you want to even remotely try to compare times with another bike. Even the same bike at the same track on the same day can cause a lot of variation in the results. Only a dyno with the proper weather station can adjust and give numbers that have relevance.

For instance a coupe of weeks ago in poor density altitude (4000 feet) the stock motored and full headered bikes were only trapping 112-115 mph and 11.70's (for his best time). My 2009 that normally traps 137-140 was just barely trapping 130 (9.80's). The bone stock gen 2 was trapping 10.70's though not sure what his MPH was? It was faster and with more MPH then another gen 2 with a heavier rider that had full system with reflash and tuning.

You are flat out going to have to do your testing on your bike on a dyno to get valid numbers to compare with.

Yes, agreed, many variables at play both with Dynos, opinions, tracks, bikes, engines, riders, elevations, air density, wind-speed, wind direction, weather, temperatures, tyres, fuel, etc, etc, etc, blah, blah, blah......

Fact or Fiction:

What I am trying to do is to be fair and reasonable and to collect some relevant factual information, preferably from this site, in an effort to improve the performance of the Cobra exhausts to as close as possible to that of a standard Vmax.

Facts as I understand them:

Gen 1 VMax Average Performance: Quarter Mile Time = 11.5 secs. Terminal Speed = 116 MPH (Ref: Haynes Manual Pg 0-10).

VMaxForum Ref thread: http://www.vmaxforum.net/showthread.php?t=44187
VmaxForum Member, standard Gen1 VMax, true 4 into 4 Exhaust, standard front headers, standard exhaust collectors, zero balance pipe, zero exhaust scavenging.
Consistent, Documented Quarter Mile Times = 11.5 Sec. Terminal Speed = 118 MPH.

So lets try and remove some of the variables, lets use a performance calculator, there are many available, you can try this at home....... pick your own......

Fact or Fiction:

Gen1 VMax weight = (281Kg) + Rider (100Kg) = 840 lbs, call it (850 lbs)

We know ET = 11.5 Secs. We know Terminal Speed = 117 MPH.

Fact or Fiction:

Weight 850 lbs + Speed 117 MPH = Estimated Horsepower 105 BHP.

Weight 850 lbs + Time 11.5 Secs = Estimated Horsepower 110.5 BHP.

Lets call it an average estimated horsepower of 108 BHP.


Now lets use the 108 BHP in the calculations:

Weight 850 lbs + 108 BHP = 116.65 MPH.

Fact or Fiction:

Interesting Summary:

Performance Calculator shows an average Vmax:
Weight 850 lbs + 108 BHP + 11.5 Secs + 116.65 MPH.

Haynes Manual shows an average VMax: 11.5 Secs + 116 MPH.

VMax forum member with 4 into 4 exhausts (Not Cobras): 11.5 + 117 MPH.

If you go by magazine articles you have to understand that many are listing corrected times and not the actual times. You have to read the specific article and see if they post the actual time slip. I can tell you that very few get much into the 11's and many stuggle to even make it out of the 12's. A light rider at a good track can run into the 10's but that's pretty dang rare.

I've made it into the 10's with a stock motored bike though header/jet kit. Many claim they have done ten second passes but most likely in better track conditions and lighter riders.

You're going to need to quit trying to use data in here to compare with as it can't be directly correlated to anything. Bikes with higher mileage can make 5-10 more HP then one with lower mileage.

If you want to establish any valid and useable data you need to pick a bike and do the comparisons to it as you do one change at a time. One time at a track is not proper data collection to establish anything with. I think if you followed the other guys thread you'll see a large difference between times with no change in configuration or setup. The bulk of his improvements I would say are due to weather conditions and experience gained.

Fact or Fiction:

Now it is starting to get interesting,
lets continue with the same Performance calculator and substitute the "Commonly claimed" "13 BHP lower BHP figures" of the "Cobra Exhausts"........


Weight 850 lbs + (108 BHP - 13 BHP) = (95 BHP) = 12.09 ET at 111.75 MPH.


If all the commonly claimed rumours are true and indeed the Cobras do lose 13 BHP compared to the standard VMax with standard exhausts, then these are the performance figures predicted as per the Performance Calculator:

Standing Start Quarter Mile = 12.09 Secs ET @ 111.75 MPH = 95 BHP.


I have seen 95 BHP documented on this site, but, the dyno could be way out... Generally many Dynos are inaccurate....

I have not seen any reliable documented Quarter Mile times or speeds of a Gen1 Vmax with Cobra Exhausts...

Generally dedicated Drag Strip timing equipment is calibrated and accurate....

:deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse::deadhorse:

:th_flipthebird:

Out on the bike this morning, first impressions, little more noisy but hardly noticeable (Was not exactly quiet in the first place...), seems to rev easier/faster but early days and only a fairly short ride....

Next step if happy with the new mods is to drill/enlarge the holes in the solid discs from 16mm to 21mm (final size)....


My thoughts/comments on direction and mods:

As discussed, very little hard data available featuring the Cobra Exhausts.....
As discussed, very hard to find hard data on VMax 4 into 4 Exhausts (Other than Cobras)......

Only really two main options with exhaust modifications, merged collectors entry or de-restricting the internals....

No evidence of anyone successfully modifying the collectors, no proof this will work, mostly merged collectors are featured/popular on 4 into 2 pipes, not 4 into 4 at all.... Often balance pipes are used for smooth running/mid range, not exactly high performance..... Expensive in time and money to modify and no history or high likelihood of success.....

On close internal inspection of the Cobras, very likely that they are highly restrictive due to bad design and cheap manufacturing practices.... History of similar modifications with very little data, cheap and easy and quick to modify.....

Interesting relevant data on 4 into 4 exhausts:

Ref: http://www.vmaxforum.net/showthread.php?t=44187

Above link shows standard engine, standard front headers, no merged collectors, no balance pipe, 4 into 4 exhausts, 1/4 mile ticket and runs at 11.5 and 117 mph, exactly the same times and speeds quoted of a standard VMax in the Haynes manual..... This suggests that this bike does not drop 13 BHP like the Cobras........


One other VMaxxer in the UK is running 4 into 4, moto-gp replica mufflers, no baffles, standard front headers, virtually standard engine, ignition upgrade, carbs upgrade pulling around 120 BHP.....

The above two examples suggest that the issue lies with the Cobra exhausts not with the merged collectors or the balance pipe......

Neither of the above two examples have the same or similar highly restrictive internal baffle system (tortuous path) of the Cobras.....

I think you have to compare apples to apples in making comparisons.

The Facts as I understand them are below:

We are looking at a true 4 into 4 exhaust with the cobras, in combination with the original standard front headers.

Using the standard VMax with standard 4 into 2 exhaust as the performance benchmark. QTR Mile time = 11.5 Secs. Terminal Speed 117 Mph.

Reference this Vmaxforum thread: http://www.vmaxforum.net/showthread.php?t=44187

This is also a true 4 into 4 exhaust, not cobras, consistently runs the same standard VMax benchmark Qtr Mile times and Terminal speeds.....
Standard engine, same standard front headers, no crossover/balance pipes/scavenging, no modified collector, very little in the way of baffles.....

Clearly the referenced VMax above consistently duplicates the standard VMax benchmark performance for QTR Mile Power and Speed.
Clearly the referenced VMax above has a true 4 into 4 exhaust like the Cobras, with standard front headers, with no modified collector box and no scavenging.
Clearly the obvious difference between the referenced VMax above and a standard VMax with Cobra exhausts is minus 13 BHP and restrictive internal Cobra baffles.....

Yes, agreed, many variables at play both with Dynos, opinions, tracks, bikes, engines, riders, elevations, air density, wind-speed, wind direction, weather, temperatures, tyres, fuel, etc, etc, etc, blah, blah, blah......

Fact or Fiction:

What I am trying to do is to be fair and reasonable and to collect some relevant factual information, preferably from this site, in an effort to improve the performance of the Cobra exhausts to as close as possible to that of a standard Vmax.

Facts as I understand them:

Gen 1 VMax Average Performance: Quarter Mile Time = 11.5 secs. Terminal Speed = 116 MPH (Ref: Haynes Manual Pg 0-10).

VMaxForum Ref thread: http://www.vmaxforum.net/showthread.php?t=44187
VmaxForum Member, standard Gen1 VMax, true 4 into 4 Exhaust, standard front headers, standard exhaust collectors, zero balance pipe, zero exhaust scavenging.
Consistent, Documented Quarter Mile Times = 11.5 Sec. Terminal Speed = 118 MPH.

Fact or Fiction:

For All of the talk and chatter about the Cobra Exhausts there does not seem to be any documented, proven, evidence that the Cobras do genuinely, actually lose the so called claimed 10 to 15 BHP compared to the stock exhaust ?????

In many cases the people peddling such claims have never owned Cobra exhausts or even ridden a Vmax with Cobras ??????

As Always, Plenty of glove puppets and spectators about......

Where is the proof ??????

The bike I dyno'd with the Cobra's was dyno'd on the same day as about a dozen other Vmax's and was so far at the bottom of the HP list that it wasn't even funny. See the chart. The closest low HP bike (not including the Fazer) was more then 10% higher and it had Kerker slip-ons on it. Most everyone else was almost 20% higher (with some 30% higher). I never got a chance to re-dyno the bike with the different mufflers though I did ride the bike through it's various changes over the years. He went from Kerker slip-ons, to the Cobra's, to a custom dual full system. I found a few pictures of the changes over the years but not a great side picture showing the Cobra's installed. They are in chronological order and you can see the final picture was it's last farewell after a bad crash. Prior to being able to dyno the bike.

I'm the one making the claim and it's from the various dyno's of these bikes with many configurations of exhaust and intakes. That's how we developed our jet kit was over many different testing stages. The only bikes ever to dyno under 100 rwhp all had the Cobra systems in place. All of our dyno testing was always done at the same facility.

Why don't you see if you can find anyone (besides the company trying to sell their cobra's) who actually has numbers greater then 110.

Fact or Fiction:

My Interest is specifically the direct (apples with apples) comparison of

(A) Standard Gen1 VMax (zero performance modifications) with Standard Exhausts

With/Against

(B) Standard Gen1 VMax (zero performance modifications) with Standard Front headers and Cobra 4 into 4 Mufflers.



Please Ref: Post # 29. Cross ref: As documented by Dale Walker.
His personal stone stock VMax = Best Pull of 99 BHP (Location Nevada).
His best ever tested stock VMaxes = 104 to 108 BHP (AVG =106 BHP) (Location California). Differences due to elevation, as stated.

Please Ref: Post # 68 Cross ref: Performance Calculator. Calculated using the following data: Weight 850 lbs (Includes Wet VMax + Rider), Quarter Mile Time of 11.5 Secs. Quarter Mile Terminal Speed of 117 MPH. (Quarter Mile Times and Speeds quoted from the Haynes Manual).
Average estimated horsepower of 108 BHP.



What I see with your information is one single VMax with Cobras pulling 96 BHP, amoungst approx 16 other bikes presumably mostly VMax, all of unknown origin, unknown modifications?

Are any (including the 96 BHP VMax) stone stock standard engines, zero performance modifications and standard front headers, stock standard rear mufflers except the 96 BHP VMax with the Cobras???